1. Field of the Invention
The present invention relates to an electric actuator, and more particularly, to an actuator for use in an electric door lock device mounted in a vehicle. Doors of the vehicle are locked or unlocked by operating the electric actuator not only by a remote control, but also by a manual operation.
2. Description of Related Art
An electric actuator of this type is proposed in Japanese Patent Publication No. 54-30316. According to the disclosure, the rotation of a motor is transmitted to a speed reducer through a centrifugal clutch, the output of the speed reducer is transmitted through a sector to an output rod which moves rectilinearly, and a door lock operation member connected to the output rod is operated. Thus, the door is locked or unlocked. During a manual locking or unlocking operation, the operation of the output rod is not transmitted to the motor through the centrifugal clutch.
According to the above-described mechanism, the clutch slides after the door lock or the door unlocking operation is performed by the motor, thus generating an uncomfortable sound. In order to prevent the generation of the sound, a limit switch for interrupting the flow of electric current is required when a predetermined locking or unlocking operation process has been performed, which causes the mechanism to be complicated and its manufacturing cost to be high.
Another mechanism is proposed in Japanese Utility Model Laid-Open Publication No. 59-74267. According to the disclosure, a cam gear driven by a motor is provided, the operation of the cam gear is transmitted to an external rotary lever through an internal rotary lever, and a door lock operation member is actuated by the external rotary lever.
This mechanism using the cam gear makes no sound, but it is necessary to make the diameter of the cam gear greater than the stroke of the rotary lever, which necessitates the provision of a large cam gear. Accordingly, the electric actuator is not compact.